| Electronic functional ceramics are the core material of passive electronic components and the important material foundation of electronic information technology.Passive electronic components have become the development bottleneck of electronic primary device technology because of the increasing miniaturization,intelligence and high-capacity development of electronic information technology.Therefore,electronic functional ceramics and their processing as well as preparation technology have gradually become one of the key core technologies that limit the development of electronic information technology.Among them,multilayer ceramic chip capacitors(MLCCs)are one of the core components widely used in numerous electronic products.Traditional perovskite-family structure ferroelectric ceramics and barium titanate-based grain boundaries layer capacitor materials have gradually been unable to meet the need of the MLCCs market.Improving the dielectric permittivity is a direct and effective method to obtain high capacitance of dielectric materials.Therefore,in order to meet the development requirements of miniaturization of electronic components and high energy storage of capacitors,the development and design of new high-permittivity,low-loss inorganic dielectric materials with good temperature and frequency stability has become an important research topic that breaks the development of electronic components "stuck neck" technology.In 2000,M.A.Subramanian et al.took the lead in reporting a non-ferroelectric copper calcium titanate(CaCu3Ti4O12,CCTO)based perovskite-related ceramics with high dielectric perlittivity(?r?104).Its dielectric permittivity could maintain good stability in the temperature range of 100-600 K because of stable phase structure.However,it is difficult to meet actual application requirements because of the high dielectric loss,poor bias voltage performance,and low breakdown electric field strength.Copper cadmium titanate(CdCu3Ti4O12,CdCTO)is a perovskite-related materials with a similar structure to CCTO,but initially exhibited poor dielectric properties(?r?409,tan ??0.093,100 kHz),which is far from the dielectric properties of CCTO materials(?r?10286,tan ??0.067,100 kHz).Why do different ACu3Ti4O12(ACTO)compounds with similar crystal structures exhibit such very different dielectric behaviors?Whether if controllable obtain the high dielectric constant behavior of CdCTO materials by means of material design,preparation technology improvement and ions modification?What are the general principles for achieving high dielectric properties of ACTO compounds?This work is intended to design a new type of CdCTO-based materials with high dielectric permittivity,low loss and good stability.Prepare high-dielectric performance CdCTO ceramics using different synthesis technologies and optimized processes;explore systematically the relationship between preparation technology,micro structure and electrical properties,and in-depth study of the physical mechanism of high-dielectric behavior in CdCTO materials.Secondly,Na1/3Cd1/3Bi1/3Cu3Ti4O12(NCBCTO)and Na1/3Cd1/3Y1/3Cu3Ti4O12(NCYCTO)with high dielectric permittivity and low dielectric loss were obtained by A-site new copper cadmium titanate-based dielectric materials designing and sintering process optimizing,and explaining its high-dielectric response of physical mechanism.Finally,regulating the dielectric properties of CdCTO materials based on A'-site ion substitution and grain boundary resistance design,B-site donor-acceptor single-ion substitution and dielectric enhancement double-ion substitution;studying systematically the influence rule of phase structure,micro structure and macroscopic electrical properties from the study of the type,content and substitution method of substituted ion,and expounding the dielectric enhancement and high dielectric response mechanism of materials.The main innovative research results obtained from experimental design and research,as well as theoretical analysis and verification were as follows:1.CdCTO materials with high dielectric permittivity are prepared using different synthesis technologies.The effects of different preparation techniques on the dielectric properties were systematically studied.The mechanism of materials synthesis reaction is proposed and the physical origin of giant dielectric properties is revealed.(1)SG-CdCTO ceramics are synthesized via a sol-gel method.The optimal conditions of CH3COOH and Ti(OC4H9)4 concentrations in the synthesis solution and water bath temperature in the process are 5.0 vol%,0.50 mol/L and 60?,respectively.SG-CdCTO materials calcined at 650? for 10 hours and sintered at 1000? for 15 hours display clear grain boundaries,less pores,and good dielectric properties:?r?1.65 × 104,tan ??0.03 at 1 kHz;good temperature stability:the temperature coefficients of the dielectric permittivity are-13.9%to 1.20%at 1 kHz and-9.10%to 3.92%10 kHz over the temperature range from-55 to 150?.(2)SS-CdCTO ceramics are synthesized using a traditional solid-state method,and systematically compare the phase structure,micro structure and electrical properties of SG-CdCTO and SS-CdCTO precursor powders and ceramics.The powders obtained by the sol-gel technology have high chemical activity,so that the crystal has a high growth power;the phase formation temperature of SG-CdCTO is at least 50-70? lower than that of SS-CdCTO.SG-CdCTO ceramics with a more uniform and dense micro structure display superior dielectric properties with a high dielectric permittivity,a low dielectric loss and a good frequency/temperature stability.(3)Giant dielectric behavior of CdCTO materials can be explained by IBLC internal barrier theory.The semiconducting grains of the material are mainly caused by the electronic hopping between Ti4+ and Ti3+;the grain boundary activation energy value is similar to that of CCTO materials,and it is mainly related to the existence of the copper-rich phase at the grain boundary.2.NCBCTO/NCYCTO materials with high dielectric permittivity are prepared through the A-site new material composition design.Its dielectric relaxation and polarization behavior are systematically explored,and the general principle of obtaining the high dielectric permittivity of ACTO materials is proposed.The research work of A-site new CdCTO materials(NCBCTO/NCYCTO)are designed and carried out by a traditional solid-state method.The dielectric properties of NCBCTO ceramics under the optimal sintering process:?r?1.5 ×104,tan ??0.04 at 1 kHz.The dielectric properties of NCYCTO material under the optimal sintering process:?r?3.8 ×104,tan ??0.065 at 1 kHz.NCBCTO/NCYCTO materials show three kinds of abnormal dielectric behaviors in the range of-180 ??500?,which are described as the contribution of grains,interface effect and oxygen doubly-ionized vacancies respectively.In addition,the extra abnormal dielectric behavior of the dielectric loss in NCYCTO materials above 300? can be described as the transition behavior of oxygen vacancy distribution from static disordered state to dynamic disordered state.The barrier height at grain boundaries of NCBCTO and NCYCTO materials are approximately 0.66?0.70 eV and 0.70?0.77 eV,which is closely related to the secondary ionization of oxygen vacancies at high temperature.3.High-resistance CdCTO-based materials are designed through A'-site components for regulating the grain boundary/grain composition and dielectric behavior.The relationship between temperature stability and dielectric relaxation,as well as grain boundary resistance and electrical properties is systematically explored and further confirm the response mechanism of semiconducting grains and insulating grain boundaries of CdCTO materials.The effect of Al3+,Mg2+ and Zn2+ion substitution on the phase structure,micro structure and electrical properties of CdCTO materials was systematically studied.Three different ions can effectively regulate the dielectric behavior of CdCTO materials;especially an appropriately small amount of Zn2+ substitutions can effectively improve the low-frequency dielectric loss.The decrease of the low-frequency dielectric loss is mainly related to grain boundary performance.The substitution materials form a high-resistance metal-oxygen local environment in the matrix lattice,replacing the low-resistance[CuO4]environment to increase the grain boundary resistance and achieving the purpose of reducing the dielectric loss tangent.The low-temperature dielectric properties of CdCTO materials substituted by Al3+,Mg2+and Zn2+ ions have shown that the temperature stability can be effectively improved by adjusting the relaxation behavior of CdMxCu3-xTi4O12 materials in different temperature regions;Zn2+ ion substitution not only succeeds in reducing the low-frequency dielectric properties,but also improving the thermal stability of the material to a certain extent.4.Refined-grain CdCTO-based ceramics are obtained by B-site single-ion substitution for regulating the resistance properties and optimizing the dielectric properties of the materials.High dielectric response mechanism is clarified,especially the correlation between low dielectric loss and resistance performance of the materials.The dielectric enhancement and high-dielectric response mechanism of different single-ion substitution CdCTO materials are systematic studied.The low-frequency dielectric loss of the CdCu3Ti3.95M0.05O12 materials with substituting by In3+,Sn4+,Ta5+ ions is significantly improved,while the CdCu3Ti3.95W0.05O12 materials is significantly increased,which is closely related to the electrical properties of grain boundaries.Among them,CdCu3Ti3.95Ta0.05O12 ceramics display superior dielectric properties with a high dielectric permittivity of ?r?2.4 ×104 and a low loss of tan ??0.064 at 1 kHz.The temperature stability of CdCu3Ti3.95M0.05O12 materials with substituting by In3+,Ta5+,W6+ is obviously improved,especially in higher temperature regions.The grain size of CdCu3Ti3.95M0.05O12 ceramics with substituting by In3+,Sn4+,Ta5+ is obviously reduced;showing higher in ?gb-1000/T,grain boundary activation energy,indicating that the grain boundary conduction behavior becomes difficult,which is also the main reason for the reduction of low-frequency dielectric loss.5.High-performance CdCTO-based materials are obtained through dielectric enhancement and B-site double ions materials design.The influence of substituted ions on the grain size,electrical resistance and dielectric properties is systematically studied,and the response mechanism of the changes in the dielectric properties caused by the substitution of different double ions has been revealed.Double ions substitution CdCu3Ti3,9875(Ag+/Zn2+/Al3+/In3++Ta5+/W6+)0.0125O12 ceramics are prepared using a traditional solid-state method.The average grain size of double ions substitution materials is significantly reduced,which is closely related to the substitution ion radius.The lattice strain energy ?Gstrain increases,and a solute drag mechanism is formed at the grain boundary,which reduces the migration driving force during the sintering process further reducing the grain boundary mobility,and effectively suppresses the crystal grain growth the final sample shows a smaller grain size.The low-frequency dielectric loss of the substituted materials is significantly reduced,which is closely related to the increase of the grain boundary resistance resulted from the increase in the volume fraction of the grain boundary.The activation energy of A2 dielectric relaxation near room temperature of the donor V-vaient Ta5+double ions substitution materials significantly decrease,indicating that the macroscopic interface effect of the substitution materials is reduced,and the temperature stability of the corresponding material is improved.The activation energy of grain boundary resistivity and dc conductivity both show increasing behavior,indicating that the height of the grain boundary barrier of the donor V-valent Ta5+ double ions substitution materials increases and the grain boundary conduction behavior becomes difficult.The donor VI-valent M6+ double ions substitution materials show lower electrical conductivity at low temperature,higher electrical conductivity at high temperature,low-temperature dielectric relaxation peak A1 shifts to high-temperature region,and improved thermal stability in high-temperature region.Therefore,there may be defect complex similar to WTi?-2Ti`Ti/2Cu`Cu and 2In`Ti-V(?) in W6+ double ions substitution materials. |
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